This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Mitosis is the fundamental process by which duplicated chromosomes are segregated during cell division. Errors in this process result in aneuploidy, which is implicated in cancer, birth defects and cell death. During mitosis, sister chromatids are physically separated by microtubules emanating from two opposing spindle poles. Microtubules attach to chromosomes via the kinetochore. Kinetochores are large protein assemblies involved in both structural and regulatory aspects of chromosome movement. These roles are central to accurate cell division, as several kinetochore components are overexpressed in cancer cells. Our goal is to uncover how kinetochores ensure that daughter cells faithfully receive their full complement of genetic material.